Benefit of repeat multiple sleep latency testing in confirming a possible narcolepsy diagnosis

The clinical diagnosis of narcolepsy is usually uncomplicated in the presence of cataplexy. Objective testing is more important in ambiguous disease. The gold-standard objective test in these cases is the multiple sleep latency test (MSLT). Repeat testing can be burdensome but is reasonable when faced with a diagnostic dilemma. However, there is limited evidence to support this approach. In this study, we assessed the diagnostic utility of a repeat MSLT in patients suspected of narcolepsy whose first MSLT result was nonconfirmatory.

Of 125 patients who underwent an MSLT between 2004 and 2009, we identified 10 (9.6%) who had undergone repeat studies. We analyzed changes in MSLT parameters while taking account of other relevant differences between testing.

Two patients (20%) met narcolepsy criteria during the second MSLT. Nine patients (90%) met sleepiness criteria (mean sleep latency <8 minutes) during the second MSLT while only 5 did during the first (P = 0.05).

We demonstrate that a repeat MSLT confirmed the diagnosis of narcolepsy in 20% of patients whose results had been nonconfirmatory on a first MSLT. This study provides support for a repeat MSLT in cases where clinical suspicion for narcolepsy is high despite an ambiguous first test.